The ITIH Protein Family: Matrix Proteins at the Interface Between Tissue Homeostasis and Disease

The inter-alpha-trypsin inhibitor (IαI) family has a long history in matrix biology. Jan J. Enghild and colleagues resolved its unusual architecture, in which heavy chains are covalently linked to the light chain bikunin via a chondroitin sulfate bridge (1991). Jean-Philippe Salier's group cloned the genes and established today's ITIH nomenclature (1996). Koji Kimata and co-workers discovered that the heavy chains become attached to hyaluronic acid (HA) (1993), and Anthony J. Day and colleagues elucidated how TSG-6 mediates this transfer (2005). For a recent overview, see Lord et al. 2020.

 Building on this foundation, our group at RWTH Aachen University has studied the ITIH heavy chains for more than two decades. ITIH proteins are large, secreted glycoproteins that organize, stabilize and remodel the extracellular matrix (ECM), and they are frequently deregulated in cancer. Through their interactions with HA, they influence tissue integrity, inflammation and wound healing, as well as how tumors communicate with their surrounding stroma.

We focus on three closely related family members: ITIH5, ITIH6, and ITIH2. Although they share a common evolutionary origin, they differ significantly in where they are expressed and the functions they perform. Our goal is to understand both the common molecular principles and the specific roles that each protein plays in cancer, cardiovascular and metabolic diseases.

ITIH5: From Tumor Suppressor to Regulator of Multiple Organs

Our group first described ITIH5 in 2004 and subsequently identified it as a class II tumor suppressor gene that is frequently silenced by epigenetic mechanisms. We have shown that ITIH5 is lost in breast, bladder, colorectal, lung, and pancreatic cancer. Functionally, ITIH5 inhibits tumor growth and metastasis . Its effects include the epigenetic reprogramming of cancer cells, a shift in TGF-β superfamily signaling, and changes in cell adhesion and migration. Some of these effects are particularly evident in three-dimensional culture models.

Beyond cancer, ITIH5 has been linked to obesity and the regulation of adipose tissue development. It has also been linked to the interaction between fat cells and blood vessel cells (2026), skin homeostasis, and cardiac remodeling following a myocardial infarction (2025).

ITIH6: A newly characterized family member

In 2025, we provided the first functional characterization of ITIH6 (also known as ITIH5L) and identified a tumor-suppressive role in cholangiocarcinoma. ITIH6 is expressed in only a few tissues, which likely explains why it remained uncharacterized for so long. Beyond cholangiocarcinoma, its functions in healthy and diseased tissues remain largely unknown and are the focus of our ongoing research.

ITIH2: The systemic partner

ITIH2 is a circulating heavy chain produced primarily by the liver. Its gene is located directly adjacent to ITIH5 on chromosome 10p14. ITIH2 could therefore link protein production in one organ to matrix remodeling in distant tissues. We are investigating how ITIH2 is processed, transported, and incorporated into tissue matrices, and whether it complements locally produced ITIH5.

Resources and Collaboration

Over the years, we have developed a range of tools for ITIH research, which we are happy to share with academic partners or use in collaborative projects:

  • Itih5 knockout mouse: The first and, to date, only phenotypically characterized constitutive Itih5 knockout line on a BALB/c background. The line is available for collaborative projects. * FFPE embedded tissues (various organs including brain) from Itih5 knock-out and WT mouse for comparison
  • Antibodies: A polyclonal anti-human ITIH5 antibody that has been comprehensively validated for immunohistochemistry on FFPE tissues (ITIH5 Pineda antibody) and published
  • Cell models: isogenic ITIH5 gain-of-function models in breast and pancreatic cancer cell lines
  • Vectors: Available for the ITIH genes ITIH2, ITIH5, and ITIH6 to generate stable overexpression lines in human cell lines and to express recombinant proteins in corresponding mammalian systems

If you are working with ITIH proteins, hyaluronic acid-rich matrices, or related disease contexts, we would be delighted to hear from you: Contact: edahlukaachende.

Outlook

Our long-term goal is to establish ITIH proteins as clinically useful biomarkers. We also aim to identify ITIH-dependent signaling pathways that could serve as therapeutic targets for modulating the tumor microenvironment and other matrix-associated diseases.